Where on your cranium is the BAHA/part you can't touch located? I'm presuming behind the ear like a normal hearing aid, but maybe not?
Most helmets, like the MICH series, OpsCore BUMP/FAST helmets, IBH, and CRYE AirFrame have open space around the ear area to accommodate radio headsets (MSA Sordin, Peltor Comtac, etc)
Here's a TC2001 for example:
even on the MICH TC2000 (pic
) the portion that goes down over the ear doesn't touch you in any way, so headsets can fit under it.
If avoiding an accidental BB strike to the hearing aid is a consideration, the TC2000 may be a better choice.
Few other pics: